What is the last object returned before the error?
What does a single "snmpgetnext" on this preceding object report?
What does "snmpgetnext" on sipCommonMethodStatsInbounds report?

The first thing to determine is *exactly* where the problem is being triggered.
Try to locate the last OID that triggers the problem, and the first one that
doesn't - even if these don't actually correspond to read MIB objects.